spring loaded platform non-suspended turntable

Let's see, if you have an unsuspended turntable on a solid unsuspended base, the structureborne vibration can get right up into the turntable platter, the tonearm and the cartridge. That being the case, I would probably opt for some kind of vibration isolation system.

One thing to consider about turntables, that's the resonant frequency of the tonearm and the cartridge and what it takes to excite the resonant frequency. As it turns out most tonearms and cartridges resonate at about 8-12 Hz. Thus, there will be no appreciable mechanical interference for the tonearm or the cartridge as long as vibrations with frequencies in the range 8-12 Hz are not present. Fair enough? But what is there to be afraid of, the acoustic energy in the room, generated by the speakers, will not go that low. And internal vibrations, produced by the motor, don't go that low. So what's the problem? The problem is the Structural Vibration produced by the Earth crust motion and traffic, subways, etc. It's the structureborne vibration that goes as low as 1-2 Hz and lower, but in particular contains frequencies in the critical range 8-12 Hz. Therefore, the most important thing to address is the Structureborne Vibration.

Consider for a moment that there are various vibration isolation designs. Of the mass on spring type, there can be vertical isolation, a combination of vertical and horizontal isolation and a combination of vertical, horizontal and rotational. There are three rotational directions of isolation - roll, rock and twist. No, I'm not talking about the Peppermint Twist. The definition of isolation in a particular direction is the ease of motion in that direction, thus good isolation in the horizontal direction would be characterized by being able to push the component easily in the horizontal directions. For turntables, which exhibit high rotational forces around the vertical axis, especially when heavy platters are involved, I suspect that isolation in the direction around the vertical axis is not desired, since rotational forces produced by the rotating platter would put the isolating system into oscillation, impacting the accuracy of the speed of the platter rotation. For that reason, I would constrain any isolation device so that only vertical and horizontal directions are addressed, keeping the rotational direction around the V axis stiff. If I'm not mistaken I believe that's exactly what Minus K did - constrain motion around the vertical axis by eliminating the isolation capability in that direction.

While it's fairly accurate that heavy rigid support structures cannot be "moved or rocked by hand," the problem arises in the way seismic vibrations manifest themselves - by moving the entire building, not only up and down and side to side but also in the rotational directions. Hel-loo! For this reason even very rigid and heavy support systems can be easily moved by the seismic type vibration. As I mentioned earlier the effectiveness of isolation is actually a function of the ease with which the component can be moved in the direction of interest. Counterintuitive, eh?